The technical field of the invention is that of devices that are used in the field of automotive safety to protect a pedestrian in the event of a head-on impact between the said pedestrian and a motor vehicle.
When a pedestrian is struck by the front of a motor vehicle it is common for the pedestrian's head to come into direct contact with the bonnet of the vehicle. This impact between the head and the bonnet causes the bonnet to deform. This deformation often goes so far as to bring the bonnet into contact with the engine block situated just underneath. The movement of the pedestrian's head is then brought to an abrupt halt by the bonnet coming into contact with the engine block and therefore experiences violent deceleration that may cause the pedestrian serious injury.
The prior art knows devices that, in the event of an impact between a pedestrian and a motor vehicle, allow the vehicle bonnet to be lifted by a certain amount so as to prevent the pedestrian's limbs and particularly his/her head from being brought to a halt, during the impact with the bonnet, by the engine block situated just under the bonnet. In the devices of the prior art, the lifting of the bonnet is performed at the rear of the bonnet, that is to say at the opposite end to the end used for opening or closing the bonnet during normal operation thereof, the bonnet remaining fixed at the front of the motor vehicle.
Patent Application EP 0 509 690 describes such a device. This device is entirely mechanical and comprises, in a first embodiment, pivoting arms allowing the bonnet to be lifted to increase the space between the bonnet and the engine block. The pivoting of the arms is obtained by moving the bonnet backwards. In the event of a head-on collision between a vehicle equipped with such a device and a pedestrian, the impact of the pedestrian with the bonnet causes a backwards translational movement of the bonnet, this translational movement being accompanied, with the aid of the pivot arms, by the lifting of the bonnet.
Patent Application WO 00/69703 also describes a mechanical device for protecting pedestrians in the event of an impact with the bonnet of a motor vehicle. This device comprises two roughly parallel arms used for opening and closing the bonnet during normal operation. At least one of these arms has a length that can vary according to the impact of the pedestrian with the bonnet. Impact with the bonnet lengthens the arm and therefore moves the bonnet away from the engine block.
These two patent applications disclose mechanical devices which are triggered when the pedestrian is in impact with the bonnet. In the first application, it is the rearwards translational movement of the bonnet, caused by the impact of the pedestrian with the bonnet, which triggers the lifting device. The pedestrian's head may therefore very well have already struck the bonnet when the bonnet-lifting device is triggered. In the second application, the impact has also already occurred when the device is actuated because the arm varies in length according to the impact of the pedestrian with the bonnet. The devices disclosed in these two applications are therefore slow and are not in any way capable of anticipating the impact of the pedestrian with the bonnet.
Patent Application GB 2 373 218 describes a device allowing the bonnet of a motor vehicle to be lifted in the event of a collision. This device comprises a structure that can be inflated using a gas generator. This structure is made of a plastically deformable material. In this device, the gas generator is coupled to a collision detector making it possible, unlike the case with the two devices described in the above two applications, to lift the bonnet very early, that is to say as the vehicle strikes the pedestrian. In this case, the bonnet is already lifted when, for example, the pedestrian's head strikes the bonnet. In such a device, it is necessary for the gas generator to be placed directly under the inflatable structure so that quick and immediate inflation of the structure can be achieved. Installing such a device will therefore entail having a significant amount of space available under the bonnet of the motor vehicle. Now, the free space in a vehicle is something that is becoming increasingly rare because, in particular, of the proliferation of devices, particularly electronic devices. In addition, this device, once used, will need to be replaced in its entirety.
Document U.S. Pat. No. 6,439,330 describes a device for lifting the bonnet of a motor vehicle. This device comprises a lifting assembly, endowed with an arm mounted to rotate at one of its ends with a leg secured to the bonnet. The second end of the arm is secured to a rotation axis mounted on a rail and able to slide along the said rail. A pyrotechnic actuator comprises a rod the end of which is mounted to rotate on the said rotation axis. Extraction of the rod under the action of the gases generated in the actuator therefore causes the translational movement of the axis along the rail, thus causing the bonnet to be lifted. The device described also has a locking device whose purpose is to immobilize the lifting assembly when the latter is at rest and therefore to prevent the bonnet from being lifted.
A device as described in this last American patent combines, in order to obtain the lifting of the bonnet, a translational movement and a rotational movement of its lifting assembly. Such kinematics therefore entails the use of a special component, in this instance that of a rail, to obtain the translational movement of the end of the arm.
Document DE 199 57 872 also discloses a device for lifting a bonnet of a motor vehicle. According to a first configuration, this device comprises a link rod mounted to rotate at its two ends with, on the one hand, at its first end, the bonnet of the vehicle and, on the other hand, at its second end, a deformable element secured to the vehicle. A pyrotechnic actuator comprises a rod the end of which is pivot-mounted at a point situated more or less at the middle of the link rod. This pyrotechnic actuator is placed under the link rod in such a way that, when it is actuated, its rod is deployed vertically to cause the link rod to pivot. In the event of an impact with a pedestrian, the deployment of the rod therefore causes the link rod to pivot about the axis situated at its second end. When the link rod has pivoted, the impact produced by the pedestrian with the bonnet causes the link rod to rock about its central point, this rocking of the link rod being allowed by virtue of the deformation of the deformable element.
According to a second configuration of this device, the link rod, at its second end, is fixed directly to the vehicle. In the event of an impact of the pedestrian with the bonnet, the link rod does not rock in pivoting about its central point where the rod is fixed, but twists on its part situated between its central point and its first end.
Such a device, unlike the one described in American document U.S. Pat. No. 6,439,330, makes it possible to get around the use of a rail in order to achieve the lifting of the bonnet. In addition, such a device uses simple operating kinematics because the lifting is obtained solely by the rotation of the link rod. However, it does not use any locking device to prevent the bonnet from being opened. In addition, in such a device, the lifting of the bonnet is performed fully and directly by the actuator rod. The force that has to be generated in order to lift the bonnet has therefore to be very high and therefore entails the use of a significant amount of pyrotechnic substance. The use of such a device may therefore prove cumbersome and bulky.